From: Andrew Morton <[email protected]>
The per-superblock dirty-inode list super_block.s_dirty is supposed to be
sorted in reverse order of each inode's time-of-first-dirtying. This is so
that the kupdate function can avoid having to walk all the dirty inodes on the
list: it terminates the search as soon as it finds an inode which was dirtied
less than 30 seconds ago (dirty_expire_centisecs).
We have a bunch of several-year-old bugs which cause that list to not be in
the correct reverse-time-order. The result of this is that under certain
obscure circumstances, inodes get stuck and basically never get written back.
It has been reported a couple of times, but nobody really cared much because
most people use ordered-mode journalling filesystems, which take care of the
writeback independently. Plus we will _eventually_ get onto these inodes even
when the list is out of order, and a /bin/sync will still work OK.
However this is a pretty important data-integrity issue for filesystems such
as ext2.
As preparation for fixing these bugs, this patch adds a pile of fantastically
expensive debugging code which checks the sanity of the s_dirty list all over
the place, so we find out as soon as it goes bad.
The debugging code is controlled by /proc/sys/fs/inode_debug, which defaults
to off. The debugging will disable itself whenever it detects a misordering,
to avoid log spew.
We can remove all this code later.
Cc: Mike Waychison <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
fs/fs-writeback.c | 77 ++++++++++++++++++++++++++++++++++++
include/linux/writeback.h | 1
kernel/sysctl.c | 8 +++
3 files changed, 86 insertions(+)
--- linux-2.6.23-rc2-mm2.orig/fs/fs-writeback.c
+++ linux-2.6.23-rc2-mm2/fs/fs-writeback.c
@@ -24,6 +24,75 @@
#include <linux/buffer_head.h>
#include "internal.h"
+int sysctl_inode_debug __read_mostly;
+
+static int __check(struct list_head *head, int print_stuff)
+{
+ struct list_head *cursor = head;
+ unsigned long dirtied_when = 0;
+
+ while ((cursor = cursor->prev) != head) {
+ struct inode *inode = list_entry(cursor, struct inode, i_list);
+ if (print_stuff) {
+ printk("%p:%lu\n", inode, inode->dirtied_when);
+ } else {
+ if (dirtied_when &&
+ time_before(inode->dirtied_when, dirtied_when))
+ return 1;
+ dirtied_when = inode->dirtied_when;
+ }
+ }
+ return 0;
+}
+
+static void __check_dirty_inode_list(struct super_block *sb,
+ struct inode *inode, const char *file, int line)
+{
+ if (!sysctl_inode_debug)
+ return;
+
+ if (__check(&sb->s_dirty, 0)) {
+ sysctl_inode_debug = 0;
+ if (inode)
+ printk("%s:%d: s_dirty got screwed up. inode=%p:%lu\n",
+ file, line, inode, inode->dirtied_when);
+ else
+ printk("%s:%d: s_dirty got screwed up\n", file, line);
+ __check(&sb->s_dirty, 1);
+ }
+ if (__check(&sb->s_io, 0)) {
+ sysctl_inode_debug = 0;
+ if (inode)
+ printk("%s:%d: s_io got screwed up. inode=%p:%lu\n",
+ file, line, inode, inode->dirtied_when);
+ else
+ printk("%s:%d: s_io got screwed up\n", file, line);
+ __check(&sb->s_io, 1);
+ }
+ if (__check(&sb->s_more_io, 0)) {
+ sysctl_inode_debug = 0;
+ if (inode)
+ printk("%s:%d: s_more_io got screwed up. inode=%p:%lu\n",
+ file, line, inode, inode->dirtied_when);
+ else
+ printk("%s:%d: s_more_io got screwed up\n", file, line);
+ __check(&sb->s_more_io, 1);
+ }
+}
+
+#define check_dirty_inode_list(sb) \
+ do { \
+ if (unlikely(sysctl_inode_debug)) \
+ __check_dirty_inode_list(sb, NULL, __FILE__, __LINE__); \
+ } while (0)
+
+#define check_dirty_inode(inode) \
+ do { \
+ if (unlikely(sysctl_inode_debug)) \
+ __check_dirty_inode_list(inode->i_sb, inode, \
+ __FILE__, __LINE__); \
+ } while (0)
+
/**
* __mark_inode_dirty - internal function
* @inode: inode to mark
@@ -122,8 +191,10 @@ void __mark_inode_dirty(struct inode *in
* reposition it (that would break s_dirty time-ordering).
*/
if (!was_dirty) {
+ check_dirty_inode(inode);
inode->dirtied_when = jiffies;
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
}
}
out:
@@ -152,6 +223,7 @@ static void redirty_tail(struct inode *i
{
struct super_block *sb = inode->i_sb;
+ check_dirty_inode(inode);
if (!list_empty(&sb->s_dirty)) {
struct inode *tail_inode;
@@ -161,6 +233,7 @@ static void redirty_tail(struct inode *i
inode->dirtied_when = jiffies;
}
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
}
/*
@@ -168,7 +241,9 @@ static void redirty_tail(struct inode *i
*/
static void requeue_io(struct inode *inode)
{
+ check_dirty_inode(inode);
list_move(&inode->i_list, &inode->i_sb->s_more_io);
+ check_dirty_inode(inode);
}
static void inode_sync_complete(struct inode *inode)
@@ -463,8 +538,10 @@ int generic_sync_sb_inodes(struct super_
if (!ret)
ret = err;
if (wbc->sync_mode == WB_SYNC_HOLD) {
+ check_dirty_inode(inode);
inode->dirtied_when = jiffies;
list_move(&inode->i_list, &sb->s_dirty);
+ check_dirty_inode(inode);
}
if (current_is_pdflush())
writeback_release(bdi);
--- linux-2.6.23-rc2-mm2.orig/include/linux/writeback.h
+++ linux-2.6.23-rc2-mm2/include/linux/writeback.h
@@ -140,5 +140,6 @@ void writeback_set_ratelimit(void);
extern int nr_pdflush_threads; /* Global so it can be exported to sysctl
read-only. */
+extern int sysctl_inode_debug;
#endif /* WRITEBACK_H */
--- linux-2.6.23-rc2-mm2.orig/kernel/sysctl.c
+++ linux-2.6.23-rc2-mm2/kernel/sysctl.c
@@ -1238,6 +1238,14 @@ static struct ctl_table fs_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "inode_debug",
+ .data = &sysctl_inode_debug,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
#if defined(CONFIG_BINFMT_MISC) || defined(CONFIG_BINFMT_MISC_MODULE)
{
.ctl_name = CTL_UNNUMBERED,
--